The present invention relates to a thread gripper and cutting device arranged at a sewing machine and comprising two resiliently cooperating clamping disks and a cutter with a cutting edge arranged at an angle to the clamping plane of the disks. A thread gripper and cutting device of this type is known, for example, from German Utility Model No. 7,405,640. In this disclosure, a first clamping disk, which projects only to a slight extent, is fixed in a recess of the machine. The second clamping disk, lying thereabove and thus projecting to a great extent, is urged against the first clamping disk by means of a spring. This second clamping disk is provided on a guide pin axially penetrating the first, fixed clamping disk. The cutter, disposed in a recess of the first clamping disk, projects with its cutting blade past the clamping plane of the clamping surface of the first clamping disk so that, when the thread is introduced in between the two disks (which means a positive lifting off of the second disk from the clamping surface of the first disk), the thread can enter into the zone of the cutting blade. In any event, a clamping and cutting device of this type thus projects considerably past the wall surface of the machine at the installation point. Consequently, it is inherently impossible to mount this device in the region of the working surface of the machine, i.e. where it would be ideally needed for severing the top and bottom threads after a sewing operation and for gripping the thread ends before the subsequent sewing step.
In contrast thereto, the present invention has the object of providing a gripper and cutting device of the aforementioned type which can be installed at the location most logical for its use, i.e. in the working surface of the machine, without impeding the sewing operation, i.e. the flow of sewing material along the working surface, and which is also at an optimum with respect to the gripping and cutting effects. For this purpose, the gripper and cutting device of the present invention is characterized by a retaining bush inserted at a spacing from the point of needle penetration in a recess of the working surface of the machine and secured against rotation. The inner shank portion of the retaining bush is integrally joined, via an axially parallel marginal web equipped with the cutter blade, with an end portion constituting the outer clamping disk and projecting, in the operative position, at least partially and, in the inoperative position, at most partially beyond the working surface. On the other hand, the inner clamping disk, which is guided in an axially movable fashion between the shank portion and the end portion along the marginal web, is urged, by means of a spring resting on the shank portion, with its outwardly oriented clamping surface, against the inwardly oriented clamping surface of the first clamping disk.
Because of this type of construction, it is possible to arrange the clamping plane, which is constituted by the contact surfaces of the two clamping disks either directly, namely only to a minor extent, above the working surface, or, in the idle position, where the plane is lowered below the working surface. Since the inner clamping disk is moved further inwardly by the inserted threads while the outer clamping disk is stationary, and also because the cutter edge terminates at this fixed disk, at most the outer clamping disk, the thickness of which is determined only by strength considerations, needs to project, in the inoperative position, beyond the working surface of the machine. In order to avoid, at least temporarily, even this slight projection of parts of the device in certain working processes, the retaining bush is suitably lowerable against the bias of a spring, by slight pressure, from the operating position of the device entirely into or below the working surface of the machine. Advantageously, the outer end of the cutter blade and thus the corresponding part of the clamping plane, determined by the contact surface of the outer clamping disk, which contact surface is advantageously slightly inclined to the working surface, lie in the plane of the working surface, while the lead-in gap between the contact surfaces of the two clamping disks is disposed at a somewhat higher level.
In case of a free-arm sewing machine, the slight projection of the end portion past the working surface in the operative position is adequate for the introduction of the thread, since the latter, after all, is pulled downwardly over the arm edge and thus can be securely guided into position between the clamping disks while lying in close contact with the working surface. In the case of flat-bed sewing machines and industrial sewing machines, such a take-off edge is not available, so that it is often difficult to hold the thread so closely above the working surface that it will pass with certainty below the slightly projecting outer clamping disk. However, on the other hand, a more pronounced, permanent projecting of the upper clamping disk would positively impede, when working with such machines, the free movement of the sewing material on the working surface. The invention makes it possible to avoid this disadvantage by providing that a dog (entrainment means) movable by an operating element, engages the retaining bush, which in turn is axially displaceable in a guide bushing. This dog can be moved from a first operating position wherein the outer clamping disk is aligned with the working surface into a second operating position wherein the clamping plane formed between the clamping disks lies at a predetermined distance above the working surface.
Suitably, the dog is, for example, a double lever engaging with one arm, through a slot in the guide bushing and in the retaining bush. The double lever is pivotable within limits about an axis in parallel to the working surface. Actually, manual operation of the dog could effect this movement of placing the clamping disks into and out of an operative position with each other. On the other hand, it so happens that the gripper and cutting device is utilized practically only with the presser foot in the lifted position. Therefore, it has proven to be especially advantageous to connect the dog with the operating element of the lifting mechanism for the presser foot in such a way that automatically, but with a delay, the retaining bush can be shifted, together with the lifting of the presser foot, by the dog toward the outside to such an extent that the clamping plane between the two clamping disks lies sufficiently far above the working surface to make the perfect introduction of the thread possible. During the lowering of the presser foot, in a likewise automatic and accelerated fashion, the retaining bush is shifted inwardly to such an extent that the suitably planar outside of the outer clamping disk comes to lie in the plane of the working surface. In many sewing machines, the lifting mechanism for the presser foot is operable via a manual lever or a knee lever. In this case, it is also possible to operatively connect the dog, by way of a suitable linkage, to this manual or knee lever. Of course, electrical or electromagnetic couplings are likewise possible.
An arrangement has proven to be especially advantageous wherein the axis of the device is located in one diagonal corner point and the needle penetration point of the machine lies in the other diagonal corner point of a square, parallel-sided with respect to the feeding (advancing) axis, imagined to be located in the feeding direction of the sewing material behind and to the left of the point of needle penetration. The cutter blade lies, in this arrangement, on the outside corner surface line, farther removed from the point of needle penetration, of the connecting web between the outer clamping disk and the shank portion of the retaining bush, this connecting web having a segment or crescent shape in cross section.
This facilitates handling of the device during introduction, gripping, and cutting of the threads and ensures a sufficiently large thread length for both sewing threads necessary for the flawless resumption of sewing.